The Bath Royal Literary and Scientific Institution will be debating The Mystery of the Wansdyke on Saturday, 22 March 2014 from 2pm to 5:30pm. See details above. The Wikipedia entry for the Wansdyke reads in part as -
 
Wansdyke (from Woden’s Dyke) is a series of early medieval defensive linear earthworks in the West Country of England, consisting of a ditch and a running embankment from the ditch spoil, with the ditching facing north. There are two main parts: an eastern dyke which runs between Savernake Forest and Morgan’s Hill in Wiltshire, and a western dyke which runs from Monkton Combe to the ancient hill fort of Maes Knoll in historic Somerset.
 
Wansdyke’s origins are unclear, but archaeological data shows that the eastern part was probably built during the 5th or 6th century. That is after the withdrawal of the Romans and before the complete takeover by the Anglo-Saxons. The ditch is on the north side, so presumably it was used by the Romano-Britons as a defence against West Saxons encroaching from the upper Thames Valley westward into what is now the West Country.
 
NB: Part of the Wansdyke is under threat from a housing development. See comment by moss above.